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Manhattan Project Jádro ve Pavel Cejnar Ústav částicové a jaderné fyziky službách Matematicko-fyzikální fakulta UK Novosemetrálka Young Minds, Praha, březen 2019 J. E. Lodge, "New triumphs in age-old quest for perfect timepiece" in Popular Science Monthly, New York, Vol. 119, No. 6, Dec. 1931, p. 53 Vazbová energie jádra R ≈ 1-8·10−15 m hmotnost „hmotnostní hmotnost hmotnost 17 3 jádra neutronů protonů schodek“ ρ ≈ 2·10 kg/m m( N ,Z ) N mn Z mp ( N ,Z ) proton −27 −27 mn=1.675·10 kg mp=1.673·10 kg Z Ekvivalence hmotnosti a energie E mc2 N Vazbová energie jádra – energie, která se uvolní, když neutron se protony a neutrony přiblíží a vytvoří vázaný systém (jádro): 2 2 2 B(N ,Z ) N mnc Z mpc m(N ,Z ) c 2 ( N ,Z )c Vazbová energie jádra V roce 1935 odvodil C.von Weizsäcker pro vazbovou energii jader jednoduchou formulku, která vysvětluje B [MeV] stabilitu jader v přírodě a ukazuje, že těžká jádra A mají menší vazbovou energii než středně těžká jádra. Carl Friedrich von Weizsäcker 1912-2007 B [MeV] A von Weiszäckerova formule 2 Z 2 (N Z)2 B a A a A3 a a V S C 1 A A A3 A N Z Vazbová energie jádra V roce 1935 odvodil C.von Weizsäcker pro vazbovou energii jader jednoduchou formulku, která vysvětluje B [MeV] stabilitu jader v přírodě a ukazuje, že těžká jádra A mají menší vazbovou energii než středně těžká jádra. Carl Friedrich von Weizsäcker 1912-2007 Obyčejné Při štěpení 1 jádra 235U hoření, např. se uvolní celkem cca C+O2→CO2, 210 MeV energie uvolní na (z toho cca 180 MeV 1 vzniklou okamžitě a cca 30 MeV molekulu při následných rozpadech) asi 1-10 eV ≈108 x víc energie 1 eV =1.6·10−19 J A N Z Řetězová reakce V r.1932 navrhli John Cockroft a Ernest Walton (vynálezci prvního urychlovače částic) uvolnění energie jádra pomocí reakce s urychlenými protony 7 4 4 p 3Li 2He 2 He . Jejich návrh zkritizoval Ernest Rutherford (objevitel atomového jádra). Podle něj energie jádra nemůže být prakticky využita. John Cockroft Ernest Walton 1897–1967 Ernest Rutherford 1903-95 1871-1937 Ernest Walton a jeho generátor, Cambridge, 1932 Řetězová reakce V r.1932 navrhli John Cockroft a Ernest Walton (vynálezci prvního urychlovače částic) uvolnění energie jádra pomocí reakce s urychlenými protony 7 4 4 p 3Li 2He 2 He . Jejich návrh zkritizoval Ernest Rutherford (objevitel atomového jádra). Leo Szilard 1898-1964 Podle něj energie jádra nemůže být prakticky využita. V r.1934 koná Enrico Fermi pokusy s bombardováním uranu neutrony (částice objevená v r.1932). V témže roce podává Leo Szilard patent předjímající neutrony n vyvolanou řetězovou reakci jader. Jeho návrh byl sice nereálný, 2n ale obsahoval zárodek správné n myšlenky… 2n n Štěpení jader neutron V prosinci 1938 nachází Otto Hahn a Fritz Strassmann (v Berlíně) ve Ida Noddack vzorcích uranu ozářeného neutrony 1896-1978 lehčí jádra (baryum). Lisa Meitner a Robert Frisch (v Dánsku) to vysvětlují jako výsledek štěpení jádra uranu, ke kterému dochází v důsledku „křehkosti“ těžkých jader neutrony dané elektrickým odpuzováním protonů… Pozn.: Možnost štěpení uranu navrhla na základě Fermiho experimentů již Otto Hahn 1879-1968 v r.1934 Ida Noddack. Lise Meitner 1878-1968 Rozdělení hmotnostních čísel štěpných Aparatura, na níž Hahn a Strassmann v Ústavu císaře Wilhelma v Berlíně objevili produktů štěpení (Deutsches Museum, Mnichov) (pro různá štěpená jádra) Štěpení jader neutron Niels Bohr („otec“ kvantové fyziky a spolutvůrce jaderné fyziky) v USA Robert Frisch nechtěně iniciuje „hon“ na přímý 1904-1979 důkaz štěpení (a hájí prvenství Frische v Kodani). Štěpení uranu se stává všeobecně známým jevem... Nature, 11.2.1939 neutrony Otto Hahn 1879-1968 Lise Meitner 1878-1968 Vzniká otázka, jakou roli hrají izotopy ퟐퟑퟖ ퟐퟑퟓ ퟗퟐ푼 a ퟗퟐ퐔, které vzhledem ke štěpení vykazují značně odlišné Nature, 18.2.1939 vlastnosti Štěpení jader neutron Niels Bohr 1885-1962 John Archibald Wheeler 1911- 2008 Štěpení jader neutron !!! Niels Bohr 1885-1962 řetězová reakce! Začátek války 1938 prosinec O.Hahn + F.Strassmann a R.Frisch + L.Meitner objevují 1939 štěpení uranu neutrony, rozebíhá leden se horečné zkoumání (N.Bohr…) březen Německo obsazuje (štěpí) Českoslo- vensko a získává jeho zásoby uranu srpen A.Einstein (na popud L.Szilárda) píše dopis prezidentu USA Rooseveltovi září začátek 2. světové války Rooseveltova odpověď odpověď Rooseveltova 1939 10. 19. dopis Rooseveltovi Einsteinův 1939 8. 2. Začátek války 1938 prosinec O.Hahn + F.Strassmann a R.Frisch + L.Meitner objevují 1939 štěpení uranu neutrony, rozebíhá leden se horečné zkoumání (N.Bohr…) březen Německo obsazuje (štěpí) Českoslo- vensko a získává jeho zásoby uranu srpen A.Einstein (na popud L.Szilárda) píše dopis prezidentu USA Rooseveltovi září začátek 2. světové války prosinec Werner Heisenberg iniciuje 1940 vývoj německého jaderného reaktoru (Uranmaschine) únor květen Německo dobývá Belgii a získává zásoby uranu v belgickém Kongu Heisenbergova tajná zpráva německému úřadu pro červen Německo dobývá Norsko zbraně (Heereswaffenamt, Army Weapons Bureau) a ovládá výrobu těžké vody "O možnosti produkce technické energie štěpením uranu" 6. 12. 1939 (část I) 20. 2. 1940 (část II) Případ Heisenberg Werner Heisenberg (vynikající teoretik, spoluzaklada- tel kvantové mechaniky) navštívil v září 1941 svého přítele Nielse Bohra v Kodani. Obsah jejich setkání dodnes nebyl zcela vyjasněn, ale Bohr jej interpretoval jako důkaz loajality Heisenberga (který sám byl před válkou nacisty napadán) nacistickému Německu. To ještě více urychlilo jaderný výzkum spojenců. Nicméně role Heisenberga v německém Werner Heisenberg 1901–1976 vojenském programu byla pravděpodobně přeceňována. V Kodani s N. Bohrem 1933, 1934, 1937 Případ Heisenberg Zürich, 18.12.1944 Pokus o zabití Heisenberga při jeho návštěvě ve Švýcarsku americkým agentem Morrisem „Moe“ Bergem. Heisenberg se ale zdál být pohlcen svým výzkumem v kvantové teorii a Berg od záměru upouští... Tabule z natáčení seriálu Génius Bomba versus reaktor Bikini test, 25. 7. 1946 Jaderná bomba „Jaderná fáze“ exploze je extrémně rychlý proces ( ≈ 1 μs ) vyžadující vysoce účinný štěpný materiál – ne 238U, ale 235U! Ten se v přírodním uranu nachází s příměsí jen 0,72 %. Uran pro bombu se proto musí obohacovat! Kritická hmota čistého 235U ve sférické geometrii je asi 50 kg (s odrá- žečem neutronů méně!). Heisenberg tuto hmotu silně nadhodnotil… (b) kritické (c) vliv neutronového (a) podkritické odrážeče množství množství Bomba versus reaktor regulační tyč moderátor moderátor moderátor moderátor palivová tyč palivová tyč U štěpení U pomalý rychlé neutron neutrony štěpení zpomalování U U zpomalování aktivní zóna moderního reaktoru Jaderný reaktor Může jako palivo využívat i neobohacený uran. Podmínkou je účinné a bezztrátové zpomalování neutronů. Nejefektivnější zpomalování neutronů probíhá na lehkých jádrech jako vodík, které však nesmí neutrony pohlco- vat – kandidáti: deuterium (těžká voda, D2O) nebo čistý uhlík (grafit). Bonus: V reaktoru s přírodním uranem vzniká plutonium 239Pu, které se dá použít v bombě podobně jako 235U ! krit.hmotnost 10 kg (ve sférické geometrii, bez odrážeče) Plutonium bylo objeveno na přelomu 1940-41 na cyklotronu v Berkeley Lab. Němci možnost výroby štěpitelného jádra v reaktoru začali zvažovat od 1941. Těžká voda 1 jádro D připadá na 6400 jader H. D20 se dá získávat mnohonásobnou elektrolýzou H20. Výroba těžké vody probíhala od r.1935 v Norsku. 1940: odvoz 185 kg těžké vody do Francie Továrna na (později do GB) – Joliot-Curie. těžkou vodu Po úplném obsazení Norska Německem je v Rjukanu, 1935 Norsk Hydro terčem diverzních akcí: říjen 1942: operace Freshman – seskok 4 norských parašutistů, přistání 2 kluzáků s 32 muži, havárie, část zahynula, ostatní zajati a popraveni… únor 1943: operace Gunnerside – seskok 6 norských parašutistů, pochod 50 km na lyžích, průnik do továrny, odpálení náloží, úspěšný návrat listopad 1943: bombardování továrny únor 1944: potopení trajektu SF Hydro, převážejícího barely D2O přes jezero Tinn. Dramatizace operace v roce 1948 Uranprojekt duben–říjen 1941 K.Diebner, A.Esau, W.Gerlach, O.Hahn, W.Bothe, K.Clusius, E.Schumann, P.Harteck, W.Heisenberg, C.v.Weiszäcker ….. Berlin Leipzig Různé návrhy experimentálního „reaktoru“ pro výzkum produkce neutronů při štěpení únor 1942 únor 1942 červen 1942 Uranprojekt – Lipská nehoda Exploze „jaderného reaktoru“ 23. 6. 1942 Příčina: chemické vznícení uranu. Důsledky: zpomalení německého výzkumu, ale paradoxně i zvýšené obavy spojenců... Snímky z natáčení seriálu Génius Uranprojekt – po 1942 Berlin říjen 1942 květen 1943 Nový design: neobohacený U (kovová forma) těžká voda Haigerloch → 1945 Spojenci rozebírají reaktor Útěk Nielse Bohra V září 1943 utíká Niels Bohr z Kodaně do Švédska, odtud je v říjnu transportován do GB a dále do USA, kde se připojuje k Manhattan Project. Cesta do GB se mu málem stala osudnou… rychlý bombardér de Havilland DH.98 Mosquito Manhattan Project Od konce 1939 USA a GB zkoumaly možnost vojenského použití uranu. Na konci 1941 se úsilí sjednotilo v rámci tzv. projektu Manhattan (1942-1946) Někteří známí fyzikové: R. Oppenheimer, N. Bohr, E. Fermi, J.von Neumann, R. Feynman, E. Wigner, L. Szilard, P. Auger, F. Bloch, I. Rabi, S. Anderson, J. Chadwick, R. Glauber, J. Cockroft, E. Condon, B. Pontecorvo, S. Ulam, N. Rosen, E. Teller, E. Segré, F. Reines, R. Peierls, A. Bohr …..………………… Představy o U-bombě kolem 1942 Manhattan Project – Feynman 1941-42: v Princetonu pracuje jako dobrovolník na vojenském výzkumu (balistika, separace uranu) 1943-45: Los Alamos, pracuje na výpočtech výtežku štěpné reakce (v Betheho skupině), ve výpočetním oddělení (koordinace „human computers“, později práce s mechanickými analogovými počítači – metoda děrných štítků), 1918 – 1988 v Oak Ridge na zabezpečení manipulace s obohaceným uranem, na vývoji uranové hybridní bomby (s moderátorem, později Von Neumann Ulam opuštěno), také jako partner v diskusích Feynman s Nielsem Bohrem Manhattan Project – jaderné reaktory 2. 12. 1942 bylo v Chicagu (pod sedadly stadionu Stagg Field ) pod vedením E. Fermiho uskutečněno první řízené štěpení uranu v reaktoru Chicago Pile-1 (přírodní uran, grafitový moderátor).
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